Light-emitting diode, light-emitting diode lamp, and illumination device

ABSTRACT

In a light-emitting diode, a plurality of dot-shaped ohmic contact electrodes are provided between a metal reflective film and a compound semiconductor layer, an ohmic electrode and a surface electrode composed of a pad portion and a plurality of linear portions connected to the pad portion are provided in that order on the opposite side of the compound semiconductor layer from the semiconductor substrate, the surface of the ohmic electrode is covered with the linear portions, the ohmic contact electrodes and the ohmic electrode are formed in positions that do not overlap with the pad portion in plane view, and among the plurality of ohmic contact electrodes, 5% or more and 40% or less of the ohmic contact electrodes are disposed in positions that overlap with the linear portions in plane view.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a light-emitting diode, a light-emitting diode lamp and an illumination device, and relates particularly to a light-emitting diode, a light-emitting diode lamp and an illumination device which are suited to high-brightness light emission.

Priority is claimed on Japanese Patent Application No. 2012-229183, filed on Oct. 16, 2012, the content of which is incorporated herein by reference.

2. Description of Related Art

Examples of known high-brightness light-emitting diodes (English abbreviation: LED) which emit red or infrared light include compound semiconductor light-emitting diodes having a light-emitting layer formed from aluminum gallium arsenide (composition formula: Al_(X)Ga_(1-X)As, 0≦X≦1) or a light-emitting layer formed from indium gallium arsenide (composition formula: In_(X)Ga_(1-X)As, 0≦X≦1). On the Other Hand, examples of known high-brightness light-emitting diodes which emit red, orange, yellow or yellow-green visible light include compound semiconductor light-emitting diodes having a light-emitting layer formed from aluminum gallium indium phosphide (composition formula Al_(X)Ga_(1-X))_(Y)In_(1-Y)P, 0≦X≦1 and 0≦Y≦1). The substrates for these compound semiconductor light-emitting diodes have generally used substrate materials such as gallium arsenide (GaAs), which are optically opaque relative to the light emitted from the light-emitting layer and do not exhibit particularly high mechanical strength.

As a result, techniques for constructing junction-type LEDs have recently been disclosed with the aim of obtaining LEDs of even higher brightness, or achieving improved mechanical strength and heat dissipation properties for these devices. These techniques involve removing the substrate material that is opaque relative to the emitted light, and joining a new support substrate composed of a material that either transmits or reflects the emitted light and exhibits excellent mechanical strength and heat dissipation properties, thereby forming a junction-type LED (for example, see Patent Documents 1 to 7).

PRIOR ART DOCUMENTS Patent Documents

[Patent Document 1] Japanese Unexamined Patent Application, First Publication No. 2001-339100

[Patent Document 2] Japanese Unexamined Patent Application, First Publication No. Hei 06-302857

[Patent Document 3] Japanese Unexamined Patent Application, First Publication No. 2002-246640

[Patent Document 4] Japanese Patent (Granted) Publication No. 2,588,849

[Patent Document 5] Japanese Unexamined Patent Application, First Publication No. 2001-57441

[Patent Document 6] Japanese Unexamined Patent Application, First Publication No. 2007-81010

[Patent Document 7] Japanese Unexamined Patent Application, First Publication No. 2006-32952

SUMMARY OF THE INVENTION

In high-brightness light-emitting diodes, in order to enable the supply of a large current to the surface electrode, the surface electrode preferably has an adequately large bonding pad. However, a problem arises in that the bonding pad absorbs the light emitted by the light-emitting unit, causing a deterioration in the light extraction efficiency. This problem of light absorption at the surface electrode pad portion is particularly marked in high-brightness light-emitting diodes.

The present invention has been developed in light of the above circumstances, and has an object of providing a light-emitting diode, a light-emitting diode lamp and an illumination device in which light absorption at the surface electrode is reduced, and a low forward voltage is achieved, while maintaining a high light emission output, by improving the positional relationship of the ohmic electrodes that sandwich the compound semiconductor layer.

In order to achieve the above object, from the viewpoint of eliminating factors causing the absorption of the emitted light, a configuration was adopted in which the growth substrate was removed and replaced with a support substrate exhibiting less light absorption. Further, in this regard, in order to reduce the light absorption at the pad (bonding pad) portion of the surface electrode, a configuration was adopted in which no light emission was generated directly beneath the surface electrode pad portion. Furthermore, the inventors discovered that in a configuration in which, among the plurality of ohmic contact electrodes dispersed across the semiconductor substrate side of the compound semiconductor layer containing the light-emitting layer, a prescribed proportion of the ohmic contact electrodes are arranged in positions which, when viewed in plane view, overlap with linear portions of the surface electrode that are connected to the pad portion, a low forward voltage could be achieved while maintaining a high light emission output, and they were therefore able to complete the present invention. Conventionally, it had been thought that employing a configuration in which the plurality of ohmic contact electrodes dispersed across the semiconductor substrate side of the compound semiconductor layer containing the light-emitting layer were arranged in positions which, when viewed in plane view, did not overlap with the linear portions of the surface electrode that were connected to the pad portion enabled the current to disperse across the entire device, and was therefore preferable.

In other words, in order to achieve the above object, the present invention employs the aspects described below.

-   -   (1) A light-emitting diode according to one aspect of the         present invention includes a junction layer, a reflective         structure containing a metal reflective film, and a compound         semiconductor layer, which contains a first cladding layer, a         second cladding layer, and a light-emitting layer sandwiched         between the first cladding layer and the second cladding layer,         provided in that order on a semiconductor substrate, wherein a         plurality of dot-shaped ohmic contact electrodes are provided         between the metal reflective film and the compound semiconductor         layer, an ohmic electrode and a surface electrode composed of a         pad portion and a plurality of linear portions connected to the         pad portion are provided in that order on the opposite side of         the compound semiconductor layer from the semiconductor         substrate, the surface of the ohmic electrode is covered with         the linear portions, the ohmic contact electrodes and the ohmic         electrode are formed in positions that do not overlap with the         pad portion in plane view, and among the plurality of ohmic         contact electrodes, 5% or more and 40% or less of the ohmic         contact electrodes are disposed in positions that overlap with         the linear portions in plane view.     -   (2) In the light-emitting diode disclosed above in (1), the pad         portion may be circular when viewed in plane view.     -   (3) In the light-emitting diode disclosed above in (1) or (2),         the linear portions may be composed of two first linear         portions, which extend in a linear direction from peripheral         edges on either side of the diameter of the pad portion, along a         line that passes through the center of the pad portion, and a         plurality of second linear portions which each extends in a         direction orthogonal to the first linear portions.     -   (4) In the light-emitting diode disclosed above in (1) or (2),         the linear portions may be composed of two second linear         portions which extend along lines that are tangent to peripheral         edges of the circular pad portion.     -   (5) In the light-emitting diode disclosed above in any one         of (1) to (4), the reflective structure may be composed of a         transparent dielectric film and a metal film.     -   (6) In the light-emitting diode disclosed above in (5), the         thickness of the transparent dielectric film may be ¾ or 5/4 of         the wavelength emitted by the light-emitting diode in the         transparent dielectric film.     -   (7) In the light-emitting diode disclosed above in (5) or (6),         the transparent dielectric film may be composed of SiO₂.     -   (8) In the light-emitting diode disclosed above in any one         of (1) to (7), the pad portion may be composed of a plurality of         circular pads.     -   (9) In the light-emitting diode disclosed above in any one         of (1) to (8), the semiconductor substrate may be composed of         any of Ge, Si, GaP and GaAs.     -   (10) In the light-emitting diode disclosed above in any one         of (1) to (9), the junction layer may include a combination of         any of an Au layer, an AuGe layer, an AuSn layer, an AuSi layer         and an AuIn layer.     -   (11) In the light-emitting diode disclosed above in any one         of (1) to (10), the light-emitting layer may be composed of any         of AlGaAs, InGaAs, GaInP, and AlGaInP.     -   (12) A light-emitting diode lamp according to another aspect of         the present invention contains the light-emitting diode         disclosed above in any one of (1) to (11).     -   (13) An illumination device according to another aspect of the         present invention is equipped with a plurality of the         light-emitting diodes disclosed above in any one of (1) to (11).

According to the light-emitting diode of the present invention, light absorption at the surface electrode is reduced, and a low forward voltage can be achieved while maintaining a high light emission output.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic cross-sectional view of a light-emitting diode of a first embodiment of the present invention.

FIG. 2A is a schematic plane view of the surface electrode of the light-emitting diode of the first embodiment of the present invention, FIG. 2B is a schematic plane view of the ohmic electrode of the light-emitting diode, FIG. 2C is a schematic plane view of the ohmic contact electrodes of the light-emitting diode, and FIG. 2D is a schematic plane view showing the overlap of the surface electrode, the ohmic electrode and the ohmic contact electrodes.

FIG. 3 is a schematic plane view illustrating another embodiment of the electrode structure of a light-emitting diode of the present invention (showing only the electrode positioning structure).

FIG. 4 is a schematic plane view illustrating another embodiment of the electrode structure of a light-emitting diode of the present invention (showing only the electrode positioning structure).

FIG. 5 is a schematic plane view illustrating another embodiment of the electrode structure of a light-emitting diode of the present invention (showing only the electrode positioning structure).

FIG. 6 is a schematic plane view illustrating another embodiment of the electrode structure of a light-emitting diode of the present invention (showing only the electrode positioning structure).

FIG. 7 is a schematic plane view illustrating another embodiment of the electrode structure of a light-emitting diode of the present invention (showing only the electrode positioning structure).

FIG. 8A is a graph illustrating the I_(F)-V_(F) characteristics of a light-emitting diode (type A) having the conventional electrode positioning structure illustrated in FIG. 9, and a light-emitting diode (type B) having the electrode positioning structure of the present invention illustrated in FIG. 2A to 2D.

FIG. 8B is a graph illustrating the I_(F)-Po characteristics of a light-emitting diode (type A) having the conventional electrode positioning structure illustrated in FIG. 9, and a light-emitting diode (type B) having the electrode positioning structure of the present invention illustrated in FIG. 2.

FIG. 9 is a schematic plane view illustrating a conventional electrode positioning structure.

FIG. 10 is a graph illustrating the relationship of the forward voltage (V_(F)) and the light emission output (Po) relative to the proportion (ratio) of ohmic contact electrodes disposed in positions which overlap with the linear portions in a light-emitting diode having the electrode positioning structure of the present invention illustrated in FIG. 2A to 2B.

FIG. 11 is a graph illustrating the relationship between the thickness of a transparent dielectric film formed from SiO₂, and the reflectance (right vertical axis) and the luminous intensity (left vertical axis).

FIG. 12 is a schematic cross-sectional view for explaining a method of manufacturing a light-emitting diode according to an embodiment of the present invention.

FIG. 13 is a schematic cross-sectional view for explaining a method of manufacturing a light-emitting diode according to an embodiment of the present invention.

FIG. 14 is a schematic cross-sectional view for explaining a method of manufacturing a light-emitting diode according to an embodiment of the present invention.

FIG. 15 is a schematic cross-sectional view for explaining a method of manufacturing a light-emitting diode according to an embodiment of the present invention.

FIG. 16 is a schematic cross-sectional view for explaining a method of manufacturing a light-emitting diode according to an embodiment of the present invention.

FIG. 17 is a schematic cross-sectional view for explaining a method of manufacturing a light-emitting diode according to an embodiment of the present invention.

FIG. 18 is a schematic cross-sectional view for explaining a method of manufacturing a light-emitting diode according to an embodiment of the present invention.

FIG. 19 is a schematic cross-sectional view for explaining a method of manufacturing a light-emitting diode according to an embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

The configurations of a light-emitting diode, a light-emitting diode lamp and an illumination device according to embodiments applying the present invention are described below by using the drawings. The drawings used in the following description have in some cases been drawn with certain features enlarged in order to assist with comprehension of those features, and as a result, the dimensional ratios between each of the structural elements in the drawings may not necessarily be the same as the actual ratios. Further, the materials and dimensions and the like presented in the following description are merely examples, and in no way limit the present invention, meaning various modifications can be made without departing from the scope of the present invention.

Light-Emitting Diode First Embodiment

FIG. 1 is a schematic cross-sectional view illustrating one example of a light-emitting diode of an embodiment applicable to the present invention.

The light-emitting diode 100 of this embodiment includes a junction layer 2, a reflective structure 9 containing a metal reflective film 4, and a compound semiconductor layer 20 containing a light-emitting layer sandwiched between a first cladding layer and a second cladding layer, provided in that order on a semiconductor substrate 1, wherein a plurality of dot-shaped ohmic contact electrodes 7 are provided between the metal reflective film 4 and the compound semiconductor layer 20, an ohmic electrode 11 and a surface electrode 12 composed of a pad portion 12 a (see FIG. 2A to 2D) and a plurality of linear portions 12 b (see FIG. 2A to 2D) connected to the pad portion are provided in that order on the opposite side of the compound semiconductor layer from the semiconductor substrate, the surface of the ohmic electrode 11 is covered with the linear portions 12 b, the ohmic contact electrodes 7 and the ohmic electrode 11 are formed in positions that do not overlap with the pad portion 12 a when viewed in plane view, and among the plurality of ohmic contact electrodes 7, at least 5% or more and 40% or less of the ohmic contact electrodes are disposed in positions that overlap with the linear portions in plane view.

In the example illustrated in FIG. 1, the ohmic contact electrodes 7 are composed of a plurality of dot-shaped conductive members, and a transparent dielectric film 8 is used to fill the spaces between the conductive members. Further, a lower current diffusion layer 5 is provided on the compound semiconductor layer 20 on the side of the transparent dielectric film 8, and an upper current diffusion layer 6 is provided on the side of the surface electrode. Furthermore, a diffusion prevention layer 3 is provided between the metal reflective film 4 and the junction layer 2.

<Compound Semiconductor Layer>

The compound semiconductor layer 20 is prepared by stacking a plurality of epitaxially grown layers, and is a stacked structure of compound semiconductors including a light-emitting layer 24.

AlGaInP layers or AlGaInAs layers or the like, which exhibit excellent light emission efficiency and have well-established substrate bonding techniques, can be used for the compound semiconductor layer 20. An AlGaInP layer is a layer formed from a material represented by a general formula (Al_(X)Ga_(1-X))_(Y)In_(1-Y)P (0≦X≦1 and 0≦Y≦1). The composition of the layer is determined in accordance with the emission wavelength of the light-emitting diode. Similarly, in the case of an AlGaInAs layer used in fabricating a light-emitting diode having a red or infrared light emission, the composition of the material is determined in accordance with the emission wavelength of the light-emitting diode.

The compound semiconductor layer 20 is an n-type or p-type conduction-type compound semiconductor in which internal pn junctions are formed AlGaInAs includes AlGaAs and GaAs and the like.

The polarity of the surface of the compound semiconductor layer 20 may be either p-type of n-type.

In the example illustrated in FIG. 1, the compound semiconductor layer 20 is composed, for example, of a contact layer 22 c, the upper current diffusion layer 6, a cladding layer 23 a, the light-emitting layer 24, a cladding layer 23 b, and the lower current diffusion layer 5. The upper current diffusion layer 6 may have a roughened surface for the purposes of light extraction. Further, the upper current diffusion layer 6 may have a structure containing two or more layers, including a surface-roughened layer.

The contact layer 22 c is a layer for lowering the contact resistance of the ohmic electrode, and is, for example, formed from Si-doped n-type GaAs, with a carrier concentration of 2×10¹⁸ cm and a layer thickness of 0.05 μm.

The upper current diffusion layer 6 is, for example, formed from Si-doped n-type (Al_(0.5)Ga_(0.5))_(0.5)In_(0.5)P, with a carrier concentration of 3×10¹⁸ cm⁻³ and a layer thickness of 5.0 μm.

The cladding layer 23 a is, for example, formed from Si-doped n-type Al_(0.45)Ga_(0.55)As, with a carrier concentration of 2×10¹⁸ cm and a layer thickness of 0.5 μm.

A layer formed from any of AlGaAs, InGaAs, GaInP and AlGaInP can be used as the light-emitting layer 24.

Specifically, the light-emitting layer 24 is composed, for example, of a stacked structure containing five undoped InGaAs layers as well layers and four (Al_(0.15)Ga_(0.85))As layers as barrier layers, wherein the thickness of each of these layers is 0.007 μm. A guide layer may be provided between the light-emitting layer 24 and the cladding layer 23 a. The guide layer is, for example, formed from (Al_(0.25)Ga_(0.75))As with a layer thickness of 0.05 μm.

The light-emitting layer 24 may have a double hetero (DH) structure, a single quantum well (SQW) structure, or a multi quantum well (MQW) structure or the like. In this description, a double hetero structure describes a structure which can confine carriers that carry radiative recombination. Further, a quantum well structure describes a structure having a well layer and two barrier layers that sandwich the well layer therebetween, wherein an SQW structure has a single well layer, and an MQW structure has two or more well layers. Methods such as the MOCVD method can be used for forming the compound semiconductor layer 20.

In order to achieve light emission having excellent monochromaticity from the light-emitting layer 24, the use of an MQW structure as the light-emitting layer 24 is preferable.

The cladding layer 23 b is, for example, formed from Mg-doped p-type Al_(0.45)Ga_(0.55)As, with a carrier concentration of 4×10¹⁷ cm and a layer thickness of 0.5 p.m. A guide layer may be provided between the light-emitting layer 24 and the cladding layer 23 b. The guide layer is, for example, formed from (Al_(0.25)Ga_(0.75))As with a layer thickness of 0.3 μm.

The lower current diffusion layer 5 is, for example, formed from Mg-doped p-type GaP, with a carrier concentration of 5×10¹⁸ cm⁻³ and a layer thickness of 2 μm.

Further, the lower current diffusion layer 5 may be formed as a stacked structure. For example, a stacked structure composed of a layer formed from Mg-doped (Al_(0.5)Ga_(0.5))_(0.5)In_(0.5)P, with a carrier concentration of 4×10¹⁷ cm⁻³ and a layer thickness of 0.05 μm, a layer formed from Mg-doped Ga_(0.7)In_(0.3)P, with a carrier concentration of 4×10¹⁷ cm⁻³ and a layer thickness of 0.02 μm, and a layer formed from Mg-doped GaP, with a carrier concentration of 5×10¹⁸ cm⁻³ and a layer thickness of 3.5 μm may be used.

The configuration of the compound semiconductor layer 20 is not limited to the structure described above, and for example, the compound semiconductor layer 20 may also have a current inhibition layer or current constriction layer for restricting the region through which the device drive current is able to flow.

(Electrode Structure)

FIG. 2A is a schematic plane view illustrating one example of the surface electrode of the present embodiment. FIG. 2B is a schematic plane view illustrating one example of the ohmic electrode of the present embodiment. FIG. 2C is a schematic plane view illustrating one example of the ohmic contact electrodes of the present embodiment. FIG. 2D is a schematic plane view showing the overlap of the surface electrode, the ohmic electrode and the ohmic contact electrodes.

<Surface Electrode>

As illustrated in FIG. 2A, the surface electrode 12 is composed of the pad portion 12 a and the linear portions 12 b connected to the pad portion 12 a.

In the present embodiment, the pad portion 12 a is circular when viewed in plane view, but other shapes besides a circular shape are also possible.

The linear portions 12 b are composed of two first linear portions 12 baa and 12 bab, which extend in mutually opposite linear directions from peripheral edges (peripheral edge portions) 12 aaa and 12 aab on either side of the diameter of the pad portion, along a line that passes through the center of the circular pad portion 12 a, and four second linear portions 12 bba, 12 bbb, 12 bca and 12 bcb, each of which extends in a direction orthogonal to the first linear portions 12 baa and 12 bab.

The second linear portions 12 bba and 12 bbb are connected to the end portions of the first linear portions 12 baa and 12 bab respectively at the opposite side from the peripheral edge portions 12 aaa and 12 aab, and are thus positioned distant from the pad portion 12 a. On the other hand, the second linear portions 12 bca and 12 bcb extend from two peripheral edge portions 12 aba and 12 abb respectively, which are positioned respectively on the two circular arcs between the two peripheral edge portions 12 aaa and 12 aab. The second linear portion 12 bca that extends from the peripheral edge portion 12 aba and the second linear portion 12 bcb that extends from the peripheral edge portion 12 abb are positioned along a single line that extends in a direction parallel to the direction of extension of the second linear portions 12 bba and 12 bbb.

The linear portions 12 b of the present embodiment are composed of two first linear portions and four second linear portions, but the invention is not limited to these numbers of portions.

The size of the pad portion 12 a, in the case of a circular pad, is typically a diameter of about 50 to 150 μm.

Further, the width of the linear portions 12 b is, for example, about 2 to 20 μm, in order to ensure that the portions have sufficient width to cover the width of the linear regions of the ohmic electrode 11. There is no necessity that all of the first linear portions and the second linear portions be the same width, but from the viewpoint of achieving uniform light extraction, the widths of those linear portions disposed in symmetrically opposing positions are preferably the same.

Examples of materials that can be used for the surface electrode include Au/Ti/Au (Au/Pt/Au, Au/Cr/Au, Au/Ta/Au, Au/W/Au, Au/Mo/Au) and the like.

<Ohmic Electrode>

As illustrated in FIG. 2B, the ohmic electrode 11 is composed of four linear regions 11 ba, 11 bb, 11 ca and 11 cb.

The ohmic electrode 11 of the present embodiment has a configuration composed of four linear regions, but the invention is not limited to this number of regions. The ohmic electrode 11 may be composed of discontinuous shapes aligned beneath the linear portions 12 b of the surface electrode, for example an array of dot-shaped electrodes.

Further, the linear regions of the ohmic electrode 11 are disposed in positions which, when viewed in plane view, do not overlap with the pad portion 12 a of the surface electrode 12, but are covered by the four second linear portions 12 bba, 12 bbb, 12 bca and 12 bcb of the linear portions 12 b of the surface electrode 12.

In other words, the two long linear regions 11 ba and 11 bb are positioned directly beneath the second linear portions 12 bba and 12 bbb respectively, and the two short linear regions 11 ca and 11 cb are positioned directly beneath the second linear portions 12 bca and 12 bcb respectively.

The reason that the ohmic electrode 11 is disposed in positions which, when viewed in plane view, do not overlap with the pad portion 12 a of the surface electrode 12 is because if the ohmic electrode 11 is disposed in a position that overlaps with the pad portion 12 a, a large proportion of the light that is emitted from directly beneath the pad portion is absorbed by the pad portion, causing a deterioration in the light extraction efficiency, which is better avoided. The material of the surface electrode 12 is a material which, when brought into direct contact with the compound semiconductor layer, is unlikely to form an ohmic junction, but rather tends to form a Schottky junction. Consequently, the resistance of the pad portion 12 a, which contacts the compound semiconductor layer without the ohmic electrode disposed therebetween, is larger than the resistance of the portions of the ohmic electrode 11. As a result, essentially no current flows beneath the pad portion 12 a, with the current flowing through the ohmic electrode 11.

The width of the linear regions that constitute the ohmic electrode 11 are typically about 1 to 10 μm in order to ensure that the regions are sufficiently narrow so as to be covered by the width of the linear portions of the surface electrode 12. There is no necessity that all of the linear regions be the same width, but from the viewpoint of achieving uniform light extraction, the widths of those linear regions disposed in symmetrically opposing positions are preferably the same.

Examples of materials that can be used for the ohmic electrode include AuGeNi, AuGe, AuNiSi and AuSi.

<Ohmic Contact Electrodes>

As illustrated in FIG. 2C, the ohmic contact electrodes 7 are composed of a plurality of conductive members which appear as dot shapes in plane view, and these conductive members are embedded inside a transparent dielectric film described below.

When the dot-shaped conductive members (namely, the dispersed conductive members) that constitute the ohmic contact electrodes 7 are viewed in plane view, 5% or more and 40% or less of the ohmic contact electrodes are disposed in positions that overlap with the linear portions 12 b of the surface electrode 12, whereas the remainder of the ohmic contact electrodes 7 are disposed in positions that do not overlap with the linear portions 12 b of the surface electrode 12.

There are no particular limitations on the shapes of the ohmic contact electrodes 7, and circular cylindrical shapes, oval cylindrical shapes, donut shapes, or linear shapes or the like may be used.

In the example illustrated in FIG. 2A to 2D, the plurality of ohmic contact electrodes 7 are arranged such that a plurality of rows of ohmic contact electrodes 7 that are aligned in parallel to the first linear portions 12 baa and 12 bab of the surface electrode 12 are aligned along a direction parallel to the second linear portions 12 bba, 12 bbb, 12 bca and 12 bcb, with each of the plurality of rows of ohmic contact electrodes 7 alternately offset by a half period.

More specifically, the number of ohmic contact electrodes 7 in each row, counting downward in order from the top of the page, is 7 (first row), 6 (second row), 4 (third row), 2 (fourth row), 4 (fifth row), 6 (sixth row) and 7 (seventh row). When viewed in plane view, 3 alternating electrodes in each of the first row and the seventh row are disposed in positions that overlap with the linear portions. Further, when viewed in plane view, 2 electrodes in each of the third row and the fifth row are disposed in positions that overlap with the linear portions. In contrast, in the second row, the sixth row and the fourth row, none of the ohmic contact electrodes overlaps with the linear portions. When viewed in plane view, those ohmic contact electrodes disposed in positions that overlap with the linear portions adopt a configuration that surrounds the pad portion 12 a.

In the example illustrated in FIG. 2A to 2D, of the total of 36 ohmic contact electrodes 7, 10 of the ohmic contact electrodes are disposed in positions that overlap with the linear portions in plane view, meaning about 28% of the ohmic contact electrodes are disposed in positions that overlap with the linear portions in plane view.

The dot-shaped conductive members that constitute the ohmic contact electrodes 7 are formed, for example, as circular cylindrical members with a diameter of about 5 to 20 μm.

Further, in a linearly arranged group of these dot-shaped conductive members, the distance between adjacent conductive members is, for example, about 5 to 40 μm.

The reason that the ohmic contact electrodes 7 are disposed in positions which, when viewed in plane view, do not overlap with the pad portion 12 a of the surface electrode 12 is because if the ohmic contact electrodes 7 are disposed in positions that overlap with the pad portion 12 a, a large proportion of the light that is emitted from directly beneath the pad portion is absorbed by the pad portion, causing a deterioration in the light extraction efficiency, which is better avoided.

Examples of materials that can be used for the ohmic contact electrodes include AuBe and AuZn and the like.

Light-Emitting Diode Other Embodiments

FIG. 3 to FIG. 7 are diagrams illustrating the electrode positioning structure in other embodiments of the present invention, with each diagram corresponding with FIG. 2D of the first embodiment.

The embodiment illustrated in FIG. 3 includes eight linear portions that correspond with the second linear portions of the surface electrode of the first embodiment. In other words, this embodiment has two long second linear portions and six short second linear portions.

In the embodiment illustrated in FIG. 3, in a similar manner to that observed in the first embodiment, the plurality of ohmic contact electrodes are arranged such that a plurality of rows of ohmic contact electrodes, which are aligned in parallel to the linear portions corresponding with the first linear portions of the surface electrode of the first embodiment, are aligned along a direction parallel to the linear portions corresponding with the second linear portions, with each of the plurality of rows of ohmic contact electrodes alternately offset by a half period.

More specifically, the number of ohmic contact electrodes in each row, counting downward in order from the top of the page, is 11 (first row), 10 (second row), 8 (third row), 4 (fourth row), 8 (fifth row), 10 (sixth row) and 11 (seventh row). When viewed in plane view, 5 alternating electrodes in each of the first row and the seventh row are disposed in positions that overlap with the linear portions. Further, when viewed in plane view, 4 electrodes in each of the third row and the fifth row are disposed in positions that overlap with the linear portions. Furthermore, one electrode in the fifth row is disposed in a position that overlaps with the linear portions. In contrast, in the second row and the sixth row, none of the ohmic contact electrodes overlaps with the linear portions.

In the example illustrated in FIG. 3, of the total of 62 ohmic contact electrodes, 18 of the ohmic contact electrodes are disposed in positions that overlap with the linear portions in plane view, meaning about 31% of the ohmic contact electrodes are disposed in positions that overlap with the linear portions in plane view.

The embodiment illustrated in FIG. 4 includes six linear portions that correspond with the second linear portions of the surface electrode of the first embodiment. In other words, this embodiment has four long second linear portions and two short second linear portions.

In the embodiment illustrated in FIG. 4, in a similar manner to that observed in the first embodiment, the plurality of ohmic contact electrodes are arranged such that a plurality of rows of ohmic contact electrodes, which are aligned in parallel to the linear portions corresponding with the first linear portions of the surface electrode of the first embodiment, are aligned along a direction parallel to the linear portions corresponding with the second linear portions, with each of the plurality of rows of ohmic contact electrodes alternately offset by a half period.

More specifically, the number of ohmic contact electrodes in each row, counting downward in order from the top of the page, is 11 (first row), 10 (second row), 11 (third row), 8 (fourth row), 8 (fifth row), 8 (sixth row), 11 (seventh row), 10 (eighth row) and 11 (ninth row). When viewed in plane view, 5 alternating electrodes in each of the first row, the third row, the seventh row and the ninth row are disposed in positions that overlap with the linear portions. Further, when viewed in plane view, 6 electrodes in the fifth row are disposed in positions that overlap with the linear portions. In contrast, in the second row, the fourth row, the sixth row and the eighth row, none of the ohmic contact electrodes overlaps with the linear portions.

In the example illustrated in FIG. 4, of the total of 88 ohmic contact electrodes, 26 of the ohmic contact electrodes are disposed in positions that overlap with the linear portions in plane view, meaning about 30% of the ohmic contact electrodes are disposed in positions that overlap with the linear portions in plane view.

The embodiment illustrated in FIG. 5 includes ten linear portions that correspond with the second linear portions of the surface electrode of the first embodiment. In other words, this embodiment has four long second linear portions and six short second linear portions.

In the embodiment illustrated in FIG. 5, in a similar manner to that observed in the first embodiment, the plurality of ohmic contact electrodes are arranged such that a plurality of rows of ohmic contact electrodes, which are aligned in parallel to the linear portions corresponding with the first linear portions of the surface electrode of the first embodiment, are aligned along a direction parallel to the linear portions corresponding with the second linear portions, with each of the plurality of rows of ohmic contact electrodes alternately offset by a half period.

More specifically, the number of ohmic contact electrodes in each row, counting downward in order from the top of the page, is 15 (first row), 14 (second row), 15 (third row), 10 (fourth row), 10 (fifth row), 10 (sixth row), 15 (seventh row), 14 (eighth row) and 15 (ninth row). When viewed in plane view, 7 alternating electrodes in each of the first row, the third row, the seventh row and the ninth row are disposed in positions that overlap with the linear portions. Further, when viewed in plane view, 8 electrodes in the fifth row are disposed in positions that overlap with the linear portions. In contrast, in the second row, the fourth row, the sixth row and the eighth row, none of the ohmic contact electrodes overlaps with the linear portions.

In the example illustrated in FIG. 5, of the total of 118 ohmic contact electrodes, 36 of the ohmic contact electrodes are disposed in positions that overlap with the linear portions in plane view, meaning about 31% of the ohmic contact electrodes are disposed in positions that overlap with the linear portions in plane view.

The embodiment illustrated in FIG. 6 includes two surface electrode pad portions, and includes three linear portions corresponding with the first linear portions of the surface electrode of the first embodiment, one of which is common to the two pads. Further, this embodiment includes 12 linear portions that correspond with the second linear portions of the surface electrode of the first embodiment. In other words, this embodiment has eight long second linear portions and four short second linear portions. The embodiment illustrated in FIG. 6 is one example of a configuration in which the pad portion is composed of a plurality of circular pads, but configurations with three or more pads are also possible.

In the embodiment illustrated in FIG. 6, in a similar manner to that observed in the first embodiment, the plurality of ohmic contact electrodes are arranged such that a plurality of rows of ohmic contact electrodes, which are aligned in parallel to the linear portions corresponding with the first linear portions of the surface electrode of the first embodiment, are aligned along a direction parallel to the linear portions corresponding with the second linear portions, with each of the plurality of rows of ohmic contact electrodes alternately offset by a half period.

More specifically, the number of ohmic contact electrodes in each row, counting downward in order from the top of the page, is 21 (first row), 20 (second row), 21 (third row), 20 (fourth row), 21 (fifth row), 20 (sixth row), 21 (seventh row), 16 (eighth row), 15 (ninth row), 16 (tenth row), 21 (eleventh row), 20 (twelfth row), 21 (thirteenth row), 20 (fourteenth row), 21 (fifteenth row), 20 (sixteenth row) and 21 (seventeenth row). When viewed in plane view, 10 alternating electrodes in each of the third row, the fifth row, the seventh row, the eleventh row, the thirteenth row and the fifteenth row are disposed in positions that overlap with the linear portions. Further, when viewed in plane view, 13 electrodes in the ninth row are disposed in positions that overlap with the linear portions. In contrast, in the first row, the second row, the fourth row, the sixth row, the eighth row, the tenth row, the twelfth row, the fourteenth row and the sixteenth row, none of the ohmic contact electrodes overlaps with the linear portions.

In the example illustrated in FIG. 4, of the total of 335 ohmic contact electrodes, 73 of the ohmic contact electrodes are disposed in positions that overlap with the linear portions in plane view, meaning about 22% of the ohmic contact electrodes are disposed in positions that overlap with the linear portions in plane view.

In the embodiment illustrated in FIG. 7, the linear portions are composed of two second linear portions which extend along lines that are tangent to the peripheral edges of the circular pad portion. In other words, this embodiment is a configuration that includes no linear portions corresponding with the first linear portions of the surface electrode of the first embodiment, but has two linear portions corresponding with the second linear portions of the surface electrode.

In the embodiment illustrated in FIG. 7, in a similar manner to that observed in the first embodiment, the plurality of ohmic contact electrodes are arranged such that a plurality of rows of ohmic contact electrodes, which are aligned in parallel to the linear portions corresponding with the first linear portions of the surface electrode of the first embodiment, are aligned along a direction parallel to the linear portions corresponding with the second linear portions, with each of the plurality of rows of ohmic contact electrodes alternately offset by a half period.

More specifically, the number of ohmic contact electrodes in each row, counting downward in order from the top of the page, is 5 (first row), 4 (second row), 4 (third row), 2 (fourth row), 4 (fifth row), 4 (sixth row) and 5 (seventh row). When viewed in plane view, 2 alternating electrodes in each of the first row, the third row, the fifth row and the seventh row are disposed in positions that overlap with the linear portions. In contrast, in the second row, the fourth row and the sixth row, none of the ohmic contact electrodes overlaps with the linear portions.

In the example illustrated in FIG. 7, of the total of 28 ohmic contact electrodes, 8 of the ohmic contact electrodes are disposed in positions that overlap with the linear portions in plane view, meaning about 29% of the ohmic contact electrodes are disposed in positions that overlap with the linear portions in plane view.

FIG. 8A and FIG. 8B illustrate the I_(F)-V_(F) characteristics and the I_(F)-Po characteristics respectively of a light-emitting diode (type A) having the conventional electrode positioning structure illustrated in FIG. 9, and a light-emitting diode (type B) having the electrode positioning structure of the present invention illustrated in FIG. 2A to 2D. In the present description, a conventional electrode positioning structure means an electrode positioning structure in which the ohmic contact electrodes are formed only in positions that do not overlap with the linear portions of the surface electrode.

As described above, in the electrode positioning structure illustrated in FIG. 2A to 2D, about 28% of the ohmic contact electrodes are disposed in positions that overlap with the linear portions when viewed in plane view.

The light-emitting diode (type A) having the conventional electrode positioning structure illustrated in FIG. 9 is similar to the present invention in that the ohmic contact electrodes are formed in positions which, when viewed in plane view, do not overlap with the pad portion of the surface electrode, but differs from the present invention in that the ohmic contact electrodes are formed only in positions that do not overlap with the linear portions of the surface electrode.

The “type B” light-emitting diode is as described below.

For the support substrate, a substrate having a Pt layer of 1 μm and an Au layer of 1 μm in that order on each surface of a Ge substrate was used.

An epitaxial wafer with an emission wavelength of 620 nm was prepared by sequentially stacking compound semiconductor layers on top of a GaAs substrate formed from Si-doped n-type monocrystalline GaAs.

In the GaAs substrate, the growth plane was inclined 15° from the (100) plane toward the (0-1-1) direction, and the carrier concentration was 1×10¹⁸ cm. The compound semiconductor layers included an n-type buffer layer formed from Si-doped GaAs, an etching stop layer formed from Si-doped (Al_(0.5)Ga_(0.5))_(0.5)In_(0.5)P, an n-type contact layer formed from Si-doped GaAs, an n-type surface surface-roughened layer formed from Si-doped (Al_(0.5)Ga_(0.5))_(0.5)In_(0.5)P, an n-type cladding layer formed from Si-doped Al_(0.5)In_(0.5)P, a light-emitting layer composed of 20 well layer/barrier layer pairs formed from (Al_(0.1)Ga_(0.9))_(0.5)In_(0.5)P/(Al_(0.5)Ga_(0.5))_(0.5)In_(0.5)P, a p-type cladding layer 23 b formed from Al_(0.5)In_(0.5)P, and the current diffusion layer 5 formed from Mg-doped p-type GaP.

The buffer layer formed from GaAs had a carrier concentration of about 1×10¹⁸ cm⁻³ and a thickness of about 0.5 μm. The etching stop layer had a carrier concentration of about 1×10¹⁸ cm⁻³ and a thickness of about 0.5 μm. The contact layer had a carrier concentration of about 1×10¹⁸ cm⁻³ and a thickness of about 0.05 μm. The surface-roughened layer had a carrier concentration of 1×10¹⁸ cm⁻³ and a thickness of about 3 μm. The upper cladding layer had a carrier concentration of about 2×10¹⁸ cm⁻³ and a thickness of about 0.5 μm. Each well layer was an undoped (Al_(0.1)Ga_(0.9))_(0.5)In_(0.5)P layer with a thickness of about 5 nm, and each barrier layer was an undoped (Al_(0.5)Ga_(0.5))_(0.5)In_(0.5)P layer with a thickness of about 5 nm. Twenty pairs of the well layer and the barrier layer were stacked alternately. The lower cladding layer had a carrier concentration of 8×10¹⁷ cm⁻³ and a thickness of about 0.5 μm.

The SiO₂ film 8 and the ohmic contact electrodes 7 formed from an AuBe alloy were formed on the current diffusion layer 5. The SiO₂ film 8 had a thickness of 0.3 μm, and the circular cylindrical conductive members that constituted the ohmic contact electrodes 7 had a diameter of 9 μm, with a distance between linearly adjacent conductive members of 43 μm. The metal reflective film 4 composed of an Au film with a thickness of 0.7 μm was formed on the SiO₂ film 8 and the ohmic contact electrodes 7 using a vapor deposition method. The diffusion prevention layer 3 composed of a Ti film with a thickness of 0.5 μm was then formed on the metal reflective film 4 using a vapor deposition method. Subsequently, the junction layer 2 formed from AuGe with a thickness of 1.0 μm was formed on the diffusion prevention layer 3 using a vapor deposition method.

The structure composed of the compound semiconductor layers and the metal reflective film and the like formed on the GaAs substrate, and the support substrate were superimposed facing each other, the resulting structure was transported into a reduced pressure apparatus, and a load of 500 kg was applied while the structure was heated at 400° C., thereby joining the two structures together to form a junction structure.

A vapor deposition method was then used to form the ohmic electrode 11 from an AuGeNi alloy, having the pattern illustrated in FIG. 2B and a thickness of 0.1 μm, on the opposite surface of the compound semiconductor layer 20 from the ohmic contact electrodes 7.

Each of the four linear regions had a width of 4 μm, the length of each of the linear regions 11 ba and 11 bb was 270 μm, and the length of each of the linear regions 11 ca and 11 cb was 85 μm.

Further, the closest distance between the linear regions 11 ba and 11 bb and the pad portion 12 a of the surface electrode 12 was 45 μm, the closest distance between the linear regions 11 ca and 11 cb and the pad portion 12 a of the surface electrode 12 was 10 μm.

The closest distance between the linear regions 11 ba and 11 bb and the pad portion 12 a of the surface electrode 12 matches the length of the first linear portions 12 baa and 12 bab of the surface electrode 12.

Using a vapor deposition method, the surface electrode 12 composed of the pad portion 12 a and the linear portions 12 b, and having the pattern illustrated in FIG. 2A and a thickness of 1.6 μm, was formed on the opposite surface of the compound semiconductor layer 20 from the ohmic contact electrodes 7, so as to cover the ohmic electrode 11.

The diameter of the pad portion 12 a was 100 μm, and the width of the linear portions 12 b was 8 μm for both the first linear portions and the second linear portions.

Further, the length of each of the first linear portions 12 baa and 12 bab was 43 μm, the length of each of the second linear portions 12 bba and 12 bbb was 270 μm, and the length of each of the second linear portions 12 bca and 12 bcb was 100 μm.

The light-emitting diode of “type A” differs from the light-emitting diode of “type B” only in the positional arrangement of the ohmic contact electrodes.

The distance between adjacent ohmic contact electrodes on each row was 12 μm.

As illustrated in FIG. 8B, in terms of the light emission output (Po), there is almost no difference between the light-emitting diode of the present invention (type B) and the conventional light-emitting diode (type A) up to a forward current (I_(F)) of 300 mA.

In contrast, as illustrated in FIG. 8A, in terms of the forward voltage (V_(F)), the light-emitting diode of the present invention (type B) is clearly superior to the conventional light-emitting diode (type A) for forward current (I_(F)) values exceeding 20 mA, with the V_(F) value for the light-emitting diode of the present invention (type B) about 7% lower than the V_(F) value of the conventional light-emitting diode (type A) up to a forward current (I_(F)) of 150 mA, and the V_(F) value for the light-emitting diode of the present invention (type B) then about 10% lower than the V_(F) value of the conventional light-emitting diode (type A) up to a forward current (I_(F)) of 300 mA.

As shown above, the light-emitting diode (type B) having the electrode positioning structure of the present invention has superior forward voltage (V_(F)) characteristics to the light-emitting diode (type A) having a conventional electrode positioning structure.

FIG. 10 is a graph illustrating the relationship of the forward voltage (V_(F)) and the light emission output (Po) relative to the proportion (ratio) of ohmic contact electrodes disposed in positions which, when viewed in plane view, overlap with the linear portions in a light-emitting diode having the electrode positioning structure of the present invention illustrated in FIG. 2A to 2D. The positional arrangement of the ohmic contact electrodes was altered so that there was no change in the configurations of the surface electrode and the ohmic electrode, and no change in the number of dot-shaped ohmic contact electrodes, with only a change in the ratio of ohmic contact electrodes disposed in positions that overlap with the linear portions.

The forward voltage (V_(F)) values are values when the forward current (I_(F)) was 300 mA, and the light emission output (Po) values represent ratios of the value at 300 mA relative to the value at 20 mA.

As illustrated in FIG. 10, as the ratio of ohmic contact electrodes disposed in positions that overlap with the linear portions increases, the forward voltage (V_(F)) decreases, but the light emission output (Po) also decreases. However, this decrease in the light emission output (Po) is small until the ratio of ohmic contact electrodes disposed in positions that overlap with the linear portions reaches about 40%.

In order to obtain an effect wherein a decrease in the forward voltage (V_(F)) of about 3% or more is obtained, while the light emission output (Po) is maintained at 90% or more of the light emission output (Po) observed when there are no ohmic contact electrodes disposed in positions that overlap with the linear portions (when the horizontal axis value in FIG. 10 is 0%), the ratio of ohmic contact electrodes disposed in positions that overlap with the linear portions must be 5% or more and 40% or less.

<Transparent Dielectric Film>

The transparent dielectric film 8 is formed so as to fill the spaces between the dot-shaped conductive members that constitute the ohmic contact electrodes 7.

Examples of materials that can be used for the transparent dielectric film 8 include ITO, SiO₂, IZO, Si₃N₄, TiO₂ and TiN.

The thickness of the transparent dielectric film 8 can be set, for example, to 0.05 to 1.0 μm.

FIG. 11 illustrates the relationship between the thickness of a transparent dielectric film formed from SiO₂, and the reflectance (right vertical axis) and the luminous intensity (left vertical axis). The horizontal axis represents the thickness of the transparent dielectric film, and is shown as a length relative to ¼n (wherein n is the refractive index of the transparent dielectric film) of the emission wavelength (620 nm was used).

The reflectance indicates results calculated by computer simulation, and the luminous intensity represent test results at a forward current (I_(F)) of 20 mA, corrected for a wavelength of 620 nm.

The computer simulation was performed under conditions including a refractive index for SiO₂ of 1.474 and a wavelength of the reflected light of 630 nm.

As illustrated in FIG. 11, it was evident that the reflectance was high when the thickness of the transparent dielectric film was λ/4n (nm), and that the reflectance was even higher when the thickness was 3λ/4n (nm) and 5λ/4n (nm).

Further, it was also evident that the luminous intensity was high when the thickness was λ/4n (nm), and was even higher when the thickness was 3λ/4n (nm) and 5λ/4n (nm). In this manner, the luminous intensity was higher when the thickness of the transparent dielectric film was 3λ/4n (nm) and 5λ/4n (nm) than when the thickness was λ/4n (nm).

Accordingly, the thickness of the transparent dielectric film is preferably thicker than λ/4n (nm), and is preferably either 3λ/4n (nm) or 5λ/4n (nm).

In the electrode positioning structure of the present invention, 5% or more and 40% or less of the ohmic contact electrodes exist in positions that overlap with (are essentially directly beneath) the linear portions of the surface electrode, and the device surface-side ohmic electrode is positioned directly beneath the linear portions. Accordingly, in a light-emitting diode having the electrode positioning structure of the present invention, the ratio with which the ohmic contact electrodes and the ohmic electrode adopt an aligned relationship in a direction orthogonal to the device surface (namely, a direction parallel to the thickness direction of the transparent dielectric film (hereafter simply referred to as “the thickness direction”)) is higher than the ratio observed in a conventional electrode positioning structure. As a result, the ratio of current that flows between the ohmic contact electrodes and the ohmic electrode in the thickness direction of the transparent dielectric film is larger than that observed for a conventional electrode positioning structure. When the current that flows between the ohmic contact electrodes and the ohmic electrode flows along the thickness direction of the transparent dielectric film, the current flows through the compound semiconductor layers along the shortest possible distance. This results in a decrease in the forward voltage (V_(F)), and therefore it is desirable that the ratio of current flowing in the thickness direction of the transparent dielectric film is high.

Further, the fact that the ratio of current that flows between the ohmic contact electrodes and the ohmic electrode, which are aligned in the thickness direction of the transparent dielectric film, is larger than that observed for a conventional electrode positioning structure means that the proportion of light emitted between the ohmic contact electrodes and the ohmic electrode that are aligned in the thickness direction of the transparent dielectric film also increases. When light emission between the ohmic contact electrodes and the ohmic electrode that are aligned in the thickness direction of the transparent dielectric film travels toward the metal reflective film in the thickness direction of the transparent dielectric film, the light contacts the ohmic contact electrodes, and it is thought that this results in a reduction in the proportion of light traveling in the thickness direction of the transparent dielectric film. In other words, it is thought that there is an increase in the proportion of light traveling through the transparent dielectric film in an oblique direction relative to the thickness direction of the transparent dielectric film. In the relationship between the thickness of the transparent dielectric layer (SiO₂) and the reflectance illustrated in FIG. 11, at a thickness of λ/4n (nm), the proportion of the variation in the reflectance upon variation in the SiO₂ film thickness is large. In contrast, when the thickness is 3λ/4n (nm) or 5λ/4n (nm), the proportion of the variation in the reflectance upon variation in the SiO₂ film thickness is much smaller. Accordingly, in the structure of the present invention, in which there is an increase in the proportion of light traveling through the transparent dielectric film in an oblique direction relative to the thickness direction of the transparent dielectric film, a thickness for the transparent dielectric layer of 3λ/4n (nm) or 5λ/4n (nm) is advantageous. In this manner, the electrode positioning structure and the thickness of the transparent dielectric film exhibit a synergistic effect. Based on test results, it was evident that the light emission characteristics were more favorable when the thickness of the transparent dielectric film was greater than λ/4n (nm), and particularly 3λ/4n (nm) or 5/4n (nm).

<Metal Reflective Film>

The metal reflective film 4 reflects light from the light emitting layer 24 in the front direction f, meaning the light extraction efficiency in the front direction f can be improved, thereby increasing the brightness of the light emitting diode.

Examples of materials that can used for the metal reflective film 4 include metals such as gold, AgPdCu alloy (APC), copper, silver, aluminum, and alloys of these metals. These materials exhibit a high degree of optical reflectance, enabling a reflectance of 90% or higher to be achieved.

The thickness of the metal reflective film 4 can be set, for example, to 0.1 to 1.0 μm.

<Diffusion Prevention Layer>

The diffusion prevention layer 3 can inhibit metal diffusing from the substrate side and reacting with the metal reflective film 4.

Examples of materials that can be used for the diffusion prevention layer 3 include nickel, titanium, platinum, chromium, tantalum, tungsten and molybdenum.

The diffusion prevention layer may also employ a combination of two or more types of metals. For example, by combining a platinum layer and a titanium layer as a first diffusion prevention layer 3 a and a second diffusion prevention layer 3 b as illustrated in FIG. 1, the barrier performance can be improved.

Even if a diffusion prevention layer is not provided, a similar function to the diffusion prevention layer can be imparted to the junction layer by adding the above materials to the junction layer.

The thickness of the diffusion prevention layer 3 can be set, for example, to 0.02 to 0.5 μm.

<Junction Layer>

The junction layer 2 is a layer used for joining the structure composed of the compound semiconductor layer 20 including the light-emitting layer 24 to a support substrate 10.

Examples of materials that can be used for the junction layer 2 include materials that are chemically stable and have a low melting point, such as Au and Au-based eutectic metals. Specific examples of gold-based eutectic metals include eutectic compositions of alloys such as AuGe, AuSn, AuSi and AuIn. Combinations of two or more types of metals, such as the combination illustrated in FIG. 1 of an AuGe layer and an Au layer as a first junction layer 2 a and a second junction layer 2 b, can also be used.

The thickness of the junction layer 2 can be set, for example, to 0.3 to 3.0 μm.

<Semiconductor Substrate>

Examples of the semiconductor substrate that constitutes the support substrate include a Ge substrate, Si substrate, GaP substrate and GaAs substrate.

<Light-Emitting Diode Lamp>

Although not illustrated in the drawings, a light-emitting diode lamp is a device in which at least one light-emitting diode 1 is mounted on the surface of a mounting substrate. More specifically, an n-electrode terminal and a p-electrode terminal are provided on the surface of the mounting substrate. Further, an n-type ohmic electrode that acts as a first electrode for the light-emitting diode and the n-electrode terminal of the mounting substrate are connected, for example, using a gold wire (wire bonding). On the other hand, a p-ohmic electrode that acts as a second electrode for the light-emitting diode and the p-electrode terminal of the mounting substrate are also connected, for example, using a gold wire. The surface of the mounting substrate on which the light-emitting diode is mounted may be sealed using an epoxy resin or the like.

<Illumination Device>

Although not illustrated in the drawings, an illumination device describes a device having at least a substrate on which wiring and/or through-holes and the like are formed, a plurality of light emitting diode lamps attached to the surface of the substrate, and a reflector or a shade which has a U-shaped cross-section, with the light emitting diode lamps provided inside the bottom of the U-shape.

[Method of Manufacturing Light-Emitting Diode]

Next is a description of a method of manufacturing the light-emitting diode according to an embodiment of the present embodiment.

<Support Substrate Production Step>

The semiconductor substrate used for supporting the structure containing the junction layer, the metal reflective film and the compound semiconductor layer is prepared by forming a layer or the like of a material suitable for joining to this structure, and then supporting the structure on this layer. In the present description, a substrate having this type of layer provided on a semiconductor substrate is termed the “support substrate”.

[1] The Case where a Ge Substrate is Used as the Semiconductor Substrate

As illustrated in FIG. 12, a layer composed of Au/Pt is formed by sequentially stacking a Pt layer 10 a and an Au layer 10 b on the upper surface 1A of a Ge substrate (semiconductor substrate) 1, and a layer composed of Pt/Au is similarly formed on the rear surface of the Ge substrate 1 by sequentially stacking a Pt layer 10 a and an Au layer 10 b, thus completing preparation of a support substrate 10 for supporting the structure containing the compound semiconductor layer 20.

The layers composed of Au/Pt are not limited to these particular materials, and other materials may be selected, provided they do not impair the effects of the present invention.

[2] The Case where an Si Substrate is Used as the Semiconductor Substrate

When an Si substrate (semiconductor substrate) is used, then in a similar manner to that described for the Ge substrate, a layer composed of Au/Pt or the like is formed on the upper surface of the Si substrate, and a layer composed of Pt/Au or the like is formed on the rear surface of the Si substrate, thus completing preparation of the support substrate 10.

The layers composed of Au/Pt are not limited to these particular materials, and other materials may be selected, provided they do not impair the effects of the present invention.

[3] The Case where a GaP Substrate is Used as the Semiconductor Substrate

When a GaP substrate (semiconductor substrate) is used, then in a similar manner to that described for the Ge substrate, a layer composed of Au/Pt or the like is formed on the upper surface of the GaP substrate, and a layer composed of Pt/Au or the like is formed on the rear surface of the GaP substrate, thus completing preparation of the support substrate 10.

The layers composed of Au/Pt are not limited to these particular materials, and other materials may be selected, provided they do not impair the effects of the present invention.

[4] The Case where a GaAs Substrate is Used as the Semiconductor Substrate

When a GaAs substrate (semiconductor substrate) is used, then in a similar manner to that described for the Ge substrate, a layer composed of Au/Pt or the like is formed on the upper surface of the GaAs substrate, and a layer composed of Pt/Au or the like is formed on the rear surface of the GaAs substrate, thus completing preparation of the support substrate 10.

The layers composed of Au/Pt are not limited to these particular materials, and other materials may be selected, provided they do not impair the effects of the present invention.

<Compound Semiconductor Layer Formation Step>

First, as illustrated in FIG. 13, a plurality of epitaxial layers are grown on one surface 21A of a growth substrate 21, thus forming an epitaxial stacked structure 30 containing the compound semiconductor layer 20.

The semiconductor substrate 21 is a substrate for forming the epitaxial stacked structure 30, and is, for example, a Si-doped n-type monocrystalline GaAs substrate in which the surface 21A is inclined 15° from the (100) plane. When AlGaInP layers or AlGaAs layers are used for the epitaxial stacked structure 30, a monocrystalline gallium arsenide (GaAs) substrate can be used as the substrate for forming the epitaxial stacked structure 30.

Examples of methods that can be used for forming the compound semiconductor layer 20 include metal organic chemical vapor deposition (MOCVD) methods, molecular beam epitaxy (MBE) methods, and liquid phase epitaxy (LPE) methods.

In the present embodiment, each layer is grown epitaxially by a reduced-pressure MOCVD method using trimethylaluminum ((CH₃)₃Al), trimethylgallium ((CH₃)₃Ga) and trimethylindium ((CH₃)₃In) as the raw materials for the group III elements.

Further, bis(cyclopentadienyl)magnesium ((C₅H₅)₂Mg) is used as a Mg doping raw material. Furthermore, disilane (Si₂H₆) is used as a Si doping raw material. Moreover, phosphine (PH₃) and arsine (AsH₃) are used as raw materials for the group V elements.

The lower current diffusion layer (GaP layer) 5 is grown, for example, at 750° C., whereas the other epitaxial growth layers are grown, for example, at 730° C.

Specifically, first, a buffer layer 22 a is formed on the surface 21A of the semiconductor substrate 21. For example, a Si-doped n-type GaAs is used as the buffer layer 22 a, with a carrier concentration of 2×10¹⁸ cm⁻³ and a thickness of 0.5 μm.

Next, in the present embodiment, an etching stop layer 22 b is formed on the buffer layer 22 a.

The etching stop layer 22 b is a layer for preventing etching of the cladding layer and the light-emitting layer when the semiconductor substrate is removed by etching, and is, for example, formed from Si-doped (Al_(0.5)Ga_(0.5))_(0.5)In_(0.5)P, with a carrier concentration of 1×10¹⁸ cm⁻³ and a thickness of 0.5 μm.

Subsequently, the contact layer 22 c is formed on the etching stop layer 22 b. The contact layer 22 c is, for example, formed from Si-doped n-type GaAs, with a carrier concentration of 2×10¹⁸ cm⁻³ and a thickness of 0.05 μm.

Next, the upper current diffusion layer 6 is formed on the contact layer 22 c. The upper current diffusion layer 6 is, for example, formed from Si-doped (Al_(0.5)Ga_(0.5))_(0.5)In_(0.5)P, with a carrier concentration of 3×10¹⁸ cm⁻³ and a thickness of 5.0 μm.

The cladding layer 23 a is then formed on the upper current diffusion layer 6. The cladding layer 23 a is, for example, formed from Si-doped n-type Al_(0.45)Ga_(0.55)As, with a carrier concentration of 2×10¹⁸ cm⁻³ and a thickness of 0.5 μm.

Next, the light-emitting layer 24 is formed on the cladding layer 23 a. The light-emitting layer 24 is, for example, formed from a stacked structure composed of five layers of undoped InGaAs as well layers and four layers of (Al_(0.15)Ga_(0.85))As as barrier layers, with the thickness of each of these layers being 0.007 μm. A guide layer may be provided between the light-emitting layer 24 and the cladding layer 23 a. The guide layer is, for example, formed from (Al_(0.25)Ga_(0.75))As with a thickness of 0.05 μm.

Subsequently, the cladding layer 23 b is formed on the light-emitting layer 24. The cladding layer 23 b is, for example, formed from Mg-doped n-type Al_(0.45)Ga_(0.55)As, with a carrier concentration of 4×10¹⁷ cm⁻³ and a thickness of 0.5 μm. A guide layer may be provided between the light-emitting layer 24 and the cladding layer 23 b. The guide layer is, for example, formed from (Al_(0.25)Ga_(0.75))As with a thickness of 0.3 μm.

Next, the lower current diffusion layer 5 is formed on the cladding layer 23 b. The lower current diffusion layer 5 is, for example, a stacked structure composed of a layer formed from Mg-doped (Al_(0.5)Ga_(0.5))_(0.5)In_(0.5)P with a carrier concentration of 4×10¹⁷ cm⁻³ and a thickness of 0.05 μm, a layer formed from Mg-doped Ga_(0.7)In_(0.3)P with a carrier concentration of 4×10¹⁷ cm⁻³ and a thickness of 0.02 μm, and a layer formed from Mg-doped GaP with a carrier concentration of 4×10¹⁷ cm⁻³ and a thickness of 3.5 μm.

A capping layer may be provided on the lower current diffusion layer 5. For example, a layer formed from undoped GaAs can be used as the capping layer. The capping layer is provided for the purpose of temporarily protecting the surface of the lower current diffusion layer 5, and is removed prior to formation of the ohmic contact electrodes.

<Ohmic Contact Electrodes Formation Step>

Next, as illustrated in FIG. 14, the ohmic contact electrodes 7 are formed on the lower current diffusion layer 5.

First, the transparent dielectric film 8 is formed across the entire surface of the lower current diffusion layer 5. Formation of the transparent dielectric film 8 is achieved, for example, by using a CVD method to form an SiO₂ film 8.

Subsequently, photolithography techniques and etching techniques are used to form a plurality of through holes in the transparent dielectric film 8 for embedding the conductive members that constitute the ohmic contact electrodes 7. This plurality of through holes is formed in positions which, when viewed in plane view, do not overlap with the pad portion 12 a of the surface electrode 12 that is formed in a subsequent step, and in positions which ensure that, when viewed in plane view, 5% or more and 40% or less of all of the ohmic contact electrodes 7 are disposed in positions that overlap with the linear portions.

More specifically, a photoresist pattern having holes that correspond with these through holes is formed on the SiO₂ film 8, and a hydrofluoric acid-based etchant is then used to remove the portions of the SiO₂ film 8 corresponding with the through holes, thereby forming the plurality of through holes in the SiO₂ film 8.

Next, a vapor deposition method or the like is used to form the AuBe alloy that functions as the material for the ohmic contact electrodes 7 in the plurality of through holes of the SiO₂ film 8.

<Metal Reflective Film Formation Step>

Next, as illustrated in FIG. 15, the metal reflective film 4 is formed on the ohmic contact electrodes 7 and the SiO₂ film 8.

In a specific example, a vapor deposition method is used to form the metal reflective film 4 from Au on the ohmic contact electrodes 7 and the SiO₂ film 8.

<Diffusion Prevention Layer Formation Step>

Next, as illustrated in FIG. 15, the diffusion prevention layer 3 is formed on the metal reflective film 4. As illustrated in FIG. 14, the diffusion prevention layer 3 may be formed from a plurality of layers (3 a and 3 b).

In a specific example, a vapor deposition method is used to form the diffusion prevention layer 3 from a Pt layer 3 a and a Ti layer 3 b on the metal reflective film 4.

<Junction Layer Formation Step>

Next, as illustrated in FIG. 15, the junction layer 2 is formed on the diffusion prevention layer 3. As illustrated in FIG. 14, the junction layer 2 may be formed from a plurality of layers (2 a and 2 b).

In a specific example, a vapor deposition method is used to form the junction layer 2, composed of an AuGe layer 2 a formed from an Au-based eutectic metal and an Au layer 2 b, on the diffusion prevention layer 3.

<Support Substrate Joining Step>

Next, as illustrated in FIG. 16, a structure 40 which includes the epitaxial stacked structure 30 and the metal reflective film 4 and the like, and the support substrate 10 formed in the support substrate production step are transported into a reduced pressure apparatus and positioned so that a joining surface 2A of the junction layer 2 and a joining surface 10A of the support substrate 10 are superimposed facing each other.

Subsequently, the reduced pressure apparatus is evacuated down to a pressure of 3×10⁻⁵ Pa, and with the superimposed structure and support substrate 10 heated at 400° C., a load of 500 kg is applied, thereby joining the joining surface 2A of the junction layer 2 and the joining surface 10A of the support substrate 10 to form a junction structure 50.

<Semiconductor Substrate and Buffer Layer Removal Step>

Next, as illustrated in FIG. 17, the semiconductor substrate 21 and the buffer layer 22 a are selectively removed from the junction structure 50 using an ammonia-based etchant.

<Etching Stop Layer Removal Step>

Subsequently, as illustrated in FIG. 18, the etching stop layer 22 b is selectively removed using a hydrochloric acid-based etchant. As a result, the compound semiconductor layer 20 containing the light-emitting layer 24 is formed.

<Ohmic Electrode Formation Step>

Next, as illustrated in FIG. 19, the ohmic electrode 11 is formed on the compound semiconductor layer 20 on the opposite surface from the ohmic contact electrodes 7.

In a specific example, a vapor deposition method is used to deposit a film of an AuGeNi alloy with a thickness of 0.1 μm across the entire surface, and photolithography techniques and etching techniques are then used to pattern the AuGeNi alloy film, thus forming the ohmic electrode 11 composed of the four linear regions 11 ba, 11 bb, 11 ca and 11 cb illustrated in FIG. 2B.

Using the mask used in the patterning of the above ohmic electrode formation step, those portions of the contact layer 22 c other than the portions directly beneath the ohmic electrode 11 are removed by etching using, for example, a mixed solution of ammonia water (NH₄OH), hydrogen peroxide (H₂O₂) and pure water (H₂O). As a result, the plane view shapes of the ohmic electrode 11 and the contact layer 22 c adopt essentially the same shape, as illustrated in FIG. 1.

The linear regions of the ohmic electrode 11 are formed in positions which, when viewed in plane view, do not overlap with the pad portion 12 a of the surface electrode 12 that is formed in a subsequent step, and in positions which are covered by the four second linear portions 12 bba, 12 bbb, 12 bca and 12 bc among the linear portions 12 b of the surface electrode 12.

<Surface Electrode Formation Step>

Next, the surface electrode 12 composed of the pad portion 12 a and the linear portions 12 b connected to the pad portion is formed on the surface of the compound semiconductor layer 20 on the opposite side from the ohmic contact electrodes 7 so as to cover the ohmic electrode 11.

In a specific example, a vapor deposition method is used to sequentially deposit an Au layer of thickness 0.3 μm, a Ti layer of thickness 0.3 μm and an Au layer of thickness 1 μm across the entire surface, and photolithography techniques and etching techniques are then used to pattern the Au/Ti/Au film to form the surface electrode 12 composed of the pad portion 12 a and the linear portions 12 b, including the two first linear portions 12 baa and 12 bab connected to the pad portion and the four second linear portions 12 bba, 12 bbb, 12 bca and 12 bcb, as illustrated in FIG. 2A.

The second linear portions are formed in positions that cover the four linear regions that constitute the ohmic electrode 11.

<Individual Segmentation Step>

Next, the light-emitting diodes on the wafer are segmented into individual devices.

Following removal of the semiconductor layer from the regions that are to be cut, the structure including the semiconductor substrate formed via the steps described above is cut with a blade dicer, for example at intervals of 350 μm, to complete fabrication of the light-emitting diode 100.

INDUSTRIAL APPLICABILITY

The light-emitting diode of the present invention can provide a light-emitting diode for which a low forward voltage can be achieved while maintaining a favorable light emission output.

DESCRIPTION OF THE REFERENCE SYMBOLS

-   1: Semiconductor substrate -   2: Junction layer -   4: Metal reflective film -   7: Ohmic contact electrode -   8: Transparent dielectric film -   9: Reflective structure -   10: Support substrate -   11: Ohmic electrode -   12: Surface electrode -   12 a: Pad portion -   12 b: Linear portion -   20: Compound semiconductor layer -   21: Growth substrate -   100: Light-emitting diode 

What is claimed is:
 1. A light-emitting diode comprising: a junction layer, a reflective structure containing a metal reflective film, and a compound semiconductor layer, which contains a first cladding layer, a second cladding layer, and a light-emitting layer sandwiched between the first cladding layer and the second cladding layer, provided in that order on a semiconductor substrate, wherein a plurality of dot-shaped ohmic contact electrodes are provided between the metal reflective film and the compound semiconductor layer, an ohmic electrode and a surface electrode composed of a pad portion and a plurality of linear portions connected to the pad portion are provided in that order on an opposite side of the compound semiconductor layer from the semiconductor substrate, a surface of the ohmic electrode is covered with the linear portions, the ohmic contact electrodes and the ohmic electrode are formed in positions that do not overlap with the pad portion in plane view, and among the plurality of ohmic contact electrodes, 5% or more and 40% or less of the ohmic contact electrodes are disposed in positions that overlap with the linear portions in plane view.
 2. The light-emitting diode according to claim 1, wherein the pad portion is circular when viewed in plane view.
 3. The light-emitting diode according to claim 1, wherein the linear portions are composed of two first linear portions, which extend in a linear direction from peripheral edges on either side of a diameter of the pad portion, along a line that passes through a center of the pad portion, and a plurality of second linear portions which each extends in a direction orthogonal to the first linear portions.
 4. The light-emitting diode according to claim 1, wherein the linear portions are composed of two second linear portions which extend along lines that are tangent to peripheral edges of a circular pad portion.
 5. The light-emitting diode according to claim 1, wherein the reflective structure is composed of a transparent dielectric film and a metal film.
 6. The light-emitting diode according to claim 5, wherein a thickness of the transparent dielectric film is ¾ or 5/4 of a wavelength emitted by the light-emitting diode in the transparent dielectric film.
 7. The light-emitting diode according to claim 5, wherein the transparent dielectric film is composed of SiO₂.
 8. The light-emitting diode according to claim 1, wherein the pad portion is composed of a plurality of circular pads.
 9. The light-emitting diode according to claim 1, wherein the semiconductor substrate is composed of any of Ge, Si, GaP and GaAs.
 10. The light-emitting diode according to claim 1, wherein the junction layer comprises a combination of any of an Au layer, an AuGe layer, an AuSn layer, an AuSi layer and an AuIn layer.
 11. The light-emitting diode according to claim 1, wherein the light-emitting layer is composed of any of AlGaAs, InGaAs, GaInP, and AlGaInP.
 12. A light-emitting diode lamp, comprising the light-emitting diode according to claim
 1. 13. An illumination device, equipped with a plurality of the light-emitting diodes according to claim
 1. 